Previous findings of this project suggest that cardiac hypertrophy induced by pressure overload is accompanied by a reduction in heat liberated during isometric contraction. Preliminary measurements of recovery heat liberation using an approximation method indicate that the increased efficiency prevails throughout the cardiac cycle and that the reduction in heat liberation during the initial period is not reversed during the recovery period. The work proposed for the following year is to measure recovery heat liberation by comparison of heat output in the presence and absence of oxygen. In addition, differences in resting heat liberation between the two preparations will be measured. With these two measurements, we will be able to assess the difference in overall efficiency between the two preparations.